This week will be a fateful one for the future of nuclear diplomacy with Iran with two major hearings in the Senate and the House followed by a Senate Banking Committee mark up of new sanctions legislation this Thursday January 29. This comes on the heels of President Obama’s State of the Union Address during which he threatened to veto new sanctions legislation and Speaker Boehner’s highly controversial invitation to Prime Minister Netanyahu to address a joint session of Congress in early March. Below we explain the current state of play on Capitol Hill and the potential implications for the negotiations.

Sanctions Legislation and This Week on Capitol Hill: Senators Kirk and Menendez are now circulating the Nuclear Weapon Free Iran Act of 2015, a tough bill to tighten sanctions on Iran if there is no nuclear deal this June. It would impose a series of cascading sanctions measures that would take effect starting only days after the summer deadline for a final deal. It would significantly tighten restrictions on Iran’s oil exports and other economic sectors, currency transactions and government officials. Additionally, it would give Congress the opportunity to review a final nuclear deal, if one is achieved, and stall its implementation. Right now it does not appear that the bill has a veto-proof majority. A competing sanctions bill that would urge punitive action on Iran, though not tied to specific “trigger” deadlines, may attract support further reducing the likelihood that the Nuclear Weapon Free Iran Act of 2015 will have sufficient backing to override a Presidential veto. The merits of the two bills will be discussed in hearings this week and the Senate Banking Committee plans to vote on the Kirk-Menendez legislation as leaders in Congress and the Administration face off over the role of Congress in nuclear diplomacy with Iran.

Implications for the Nuclear Negotiations: The parties are attempting to negotiate a political framework on the key issues by the end of March 2015 and a final comprehensive deal by late June 2015. Over the past couple of weeks, the negotiations appear to have taken a more serious and urgent tone with the primary focus shifting from multilateral meetings between Iran and the P5+1 to bilateral negotiations between Iran and the United States. This is a good sign as the United States and Iran are the two most important players in this drama, and indeed the November 2013 breakthrough on the Joint Plan of Action came primarily through bilateral negotiations.

Still, there are real gaps on three key issues: (1) the scope and size of Iran’s uranium enrichment program including the size of its uranium stockpile as well as the number and type of centrifuges it can maintain; (2) the duration of the agreement, with the United States aiming for 15 years and Iran asking for 5-7; and (3) the timing and sequencing of sanctions relief, with the Iranians asking for more up front and the P5+1 seeking a phased approach over a longer timeframe. The Iranians have also expressed significant concerns about the Obama Administration’s ability to deliver on sanctions relief, arguing that even if the President agrees to lift sanctions, Congress will not let him.

Pressure from the Hill could affect the negotiations in multiple ways. In the scenario that is likely to be least detrimental to nuclear diplomacy, the current confrontation on the Hill ends with a clear victory for President Obama, but one that signals to Iran that time and patience is running out with Congress. This outcome would increase the urgency on all sides to close the gaps and agree on a deal by the deadline. However, it would also signal to the Iranian negotiators that President Obama remains in control of this policy, giving them greater confidence that in the event of a deal he would be able to deliver on his promise of sanctions relief. Indeed, Hillary Clinton’s comments this week in support of the President’s approach were also an important signal to Tehran demonstrating that in the event of a deal the most likely nominee for the Democratic party in the 2016 election would support continued implementation of an agreement including sanctions relief.

However, if Congress goes too far now and passes new sanctions legislation in advance of the end of March deadline, and overrides a Presidential veto, it would signal to the Iranians that President Obama likely couldn’t deliver on sanctions relief in the event of an agreement. It would give the Iranians an opportunity to walk away from the talks and put the blame on the United States, possibly causing the international sanctions coalition, and the nuclear negotiations, to break apart. It would also undermine President Rouhani at home in his own debates with Iranian hardliners and reaffirm Supreme Leader Ali Khamenei’s publicly stated suspicions that the United States has no intention of lifting sanctions. Fortunately, this scenario appears less likely.

If Congress holds off on sanctions for the moment, and a breakthrough on a political framework agreement is not reached by the end of March, then holding off sanctions might no longer be possible or desirable. At that point the Obama Administration needs to decide if it wants to: 1) Continue to try to hold off new sanctions from Congress and negotiate a comprehensive agreement; 2) Pursue a new interim agreement that includes additional steps beyond the JPOA that further roll back Iran’s nuclear program for greater sanctions relief; or 3) Engage with Congress and negotiate a new sanctions package that would increase the pressure on Iran as the negotiations move towards the late June deadline.

Ms. Rosenberg and Mr. Goldenberg are available for interviews. To arrange an interview, please contact Neal Urwitz at nurwitz@cnas.org or call 202-457-9409.